In vertical furnaces used for semiconductor wafer processing, a wafer boat may be used for accommodating a stack of vertically spaced apart wafers. Typically, as shown in FIG. 1, a wafer boat 100 comprises three or more vertical rods 110 which extend between a top member 120 and a bottom member 130. In the example of FIG. 1, three rods 110 are shown: two side rods 110A and one back rod 110B. In the rods, vertically spaced apart recesses 150 are formed at corresponding heights, facing inwardly (i.e. generally towards a central axis of the wafer boat 100). Each recess serves as a support arranged for engaging a circumferential side portion of a wafer, and recesses at a same height define a wafer accommodation for receiving and supporting a wafer in a substantially horizontal orientation. Wafers can be inserted into and removed from the boat at an open side of the boat, opposite the back rod 110B.
A problem with known wafer boats is that damage may occur on the wafer at the point of contact between the wafer and the boat. Due to different thermal expansion of the wafer and the boat, for instance, the wafer may move relative to the recess, resulting in scratches.
In the art, support members are proposed that have a convex support surface to minimize contact stresses in the wafer at the support point. However, boats having these support members are difficult to manufacture and require elaborate machining. In some proposals the wafer support members are separately machined for ease of machining and then mounted in the wafer boat which is also a complex procedure and construction.